The present invention relates to an electrical switch.
The invention is particularly but not exclusively concerned with a normally-closed pushbutton switch. Electrical switches of this type are in abundant use, in which a separate moving contact may have opposite parts for contact with respective fixed contacts as two contact points. The contact point that is first to make and last to break is subject to contact arcing and flashover, especially for heavy current application, but it is often uncertain as to which one of the contact points will take the brunt, or a relatively complicated mechanism is needed.
The subject invention seeks to mitigate or at least alleviate such a shortcoming by providing an improved electrical switch.
According to the invention, there is provided an electrical switch comprising a casing, first and second fixed contacts, and a moving contact having first and second parts for contact with the first and second fixed contacts respectively. A spring is included to resiliently bias the moving contact into contact with both fixed contacts. There is also an operating member supported by the casing for movement between first and second positions to cause the moving contact to move into contact with and out of contact from the fixed contacts respectively. The operating member and the spring act upon the moving contact at respective positions that are offset from each other. The moving contact is pivotable by the operating member in one direction to separate its first part from the first fixed contact and subsequently in an opposite direction to also separate its second part from the second fixed contact.
Preferably, the casing includes a support for engagement by the first part of the moving contact to enable the moving contact to pivot in said opposite direction.
More preferably, the support is situated on one side of the first part of the moving contact opposite a part of the first fixed contact with which the first moving contact part is to make contact.
More preferably, the support comprises a heat sink.
In a preferred embodiment, the operating member and the spring act upon the moving contact along respective substantially co-parallel axes that are offset from each other.
In a specific construction, the moving contact comprises a lever having opposite ends as its first and second parts.
As an example, the spring comprises a compression coil spring.
It is preferred that the operating member includes a spring engaging the moving contact.
As an example, the operating member comprises a pushbutton.
Preferably, the aforesaid electrical switch is a normally-closed switch in which upon release of the operating member the moving contact is biassed into contact with both fixed contacts.